Abnormal positive potentials in round window electrocochleography.

OBJECTIVE

To describe an atypical waveform, termed an abnormal positive potential (APP), on round window electrocochleograms (RW ECochG) of children and to relate its occurrence to clinical history.

STUDY DESIGN

APPs were identified prospectively, and a retrospective analysis was made of these patients' clinical histories, audiograms, and auditory outcomes (hearing aid, cochlear implant, or nonauditory communication)

SETTING

Tertiary referral teaching hospital, day surgery and clinics.

PATIENTS

All 431 children <110 months of age suspected of a severe to profound hearing loss who underwent RW ECochG from January 1993 to August 1997.

INTERVENTION

Diagnostic RW ECochG for auditory threshold estimation.

MAIN OUTCOME MEASURE

The presence on the RW ECochG of the APP: an early positive potential in the absence of a compound action potential (CAP).

RESULTS

An APP was observed in 34 children. The APP was most marked in response to clicks and 8-kHz tones. The APP click threshold averaged 70 dB hearing loss. The brainstem evoked potential of these children showed an absence of waves, or a broad positive wave with no subsequent waves. Twenty-nine of 30 behavioral audiograms obtained were indicative of severe to profound hearing loss. Auditory outcomes were available from 26 children; 45% of them derived no help from a hearing aid, and 8 children received a cochlear implant. Clinical factors frequently associated with APP were prematurity in combination with kemicterus or hypoxia.

CONCLUSIONS

APP thresholds were lower than neural thresholds or behavioral thresholds. Children with APP need close follow-up, because half of those studied needed nonauditory strategies to develop effective communication.